Critical Warning: Ethosuximide is Appropriate for Absence Seizures, Not Focal Seizures
If this patient truly has focal (partial) seizures, ethosuximide should never have been started in the first place, as it is only effective for absence seizures and carbamazepine is indeed the appropriate choice for focal seizures. 1 However, if the patient actually has absence seizures (not focal seizures), switching to carbamazepine would be a dangerous error, as carbamazepine can exacerbate absence seizures and trigger myoclonic jerks. 2, 3, 4
Verify Seizure Type Before Proceeding
- Confirm the actual seizure type through EEG and clinical history before making any medication changes. 5
- If generalized spike-and-wave complexes are present on EEG, the patient has absence seizures, not focal seizures, and carbamazepine is contraindicated. 2, 4
- Carbamazepine is only effective for partial (focal) seizures and generalized tonic-clonic seizures, never for absence seizures. 6, 1
If Confirmed Focal Seizures: Transition Protocol
Ethosuximide Taper
- Taper ethosuximide gradually over 2-4 weeks while simultaneously initiating carbamazepine. 7
- Reduce ethosuximide dose by 25% every 5-7 days while monitoring for breakthrough seizures. 7
- Do not abruptly discontinue, as this increases seizure risk. 7
Carbamazepine Initiation and Titration
- Start carbamazepine at 200 mg at bedtime to minimize dizziness and drowsiness. 8, 6
- Increase by 200 mg every 7 days as tolerated. 8
- Target maintenance dose: 400-1200 mg/day divided into 2-3 doses (never single daily dosing due to short half-life). 8, 6
- Therapeutic blood levels should be 4-8 mcg/mL. 8
Pre-Treatment Screening
- Perform HLA-B*15:02 genetic screening before starting carbamazepine, particularly in patients of Asian descent, to reduce Stevens-Johnson syndrome risk. 8
Laboratory Monitoring Requirements
- Obtain baseline complete blood count (CBC) and liver function tests (LFTs) before starting carbamazepine. 8, 6
- Repeat CBC and LFTs monthly for the first 3 months (highest risk period for aplastic anemia). 8, 6
- After 3 months, monitor every 3-6 months if stable. 8
- Monitor for leukopenia (may be transient) versus aplastic anemia (rare but potentially fatal). 6
Clinical Monitoring During Transition
- Assess for seizure activity at each dose reduction of ethosuximide and each dose increase of carbamazepine. 7
- Monitor for carbamazepine side effects: fatigue, dizziness, ataxia, double vision, nausea, vomiting. 6
- If withdrawal symptoms or breakthrough seizures occur, slow the taper and re-escalate to the last effective dose. 7
Common Pitfalls to Avoid
- Never use carbamazepine for absence seizures—it will worsen them. 2, 3, 4
- Do not rush the ethosuximide taper in patients with poorly controlled seizures. 7
- Avoid single daily dosing of carbamazepine due to excessive peak levels and inadequate trough coverage. 6
- Do not skip HLA-B*15:02 screening in at-risk populations. 8
- Counsel female patients that carbamazepine decreases oral contraceptive effectiveness; alternative contraception is required. 8